The researchers have called for more accurate food labelling so people know what species they are eating.

“The discovery of endangered hammerhead sharks highlights how widespread the sale of declining species really is – even reaching Europe and the UK,” said Dr Andrew Griffiths, of the University of Exeter

Fishing for spiny dogfish has been prohibited in most circumstances under EU rules. The spiny dogfish found in many chip shop samples could have been sourced from more sustainable stocks elsewhere, but it highlights the problems of selling shark meat under “umbrella” terms that cover multiple species.

“It’s almost impossible for consumers to know what they are buying,” said first author Catherine Hobbs, also of the University of Exeter.

“There are also health issues. Knowing what species you are buying could be important in terms of allergies, toxins, mercury content and the growing concern over microplastics in the marine food chain.

“Our findings demonstrate the need for more informative and accurate seafood labelling.”

As well as spiny dogfish, the researchers found species including starry smooth-hounds, nursehounds and blue sharks on sale in fishmongers and chip shops.

Through “DNA barcoding”, the study analysed 78 samples from chip shops and 39 from fishmongers, mostly in southern England, as well as 10 fins from a wholesaler.

It also analysed 30 fins seized by the UK Border Force on their way from Mozambique to Asia. These came from species including bull sharks.

Miss Hobbs added: “Knowledge of shark species consumption in the UK, especially those of prohibited species and those of high conservation concern, enhances our ability to address the decline in shark populations.”

The paper, published in the journal Scientific Reports, is entitled: “Using DNA Barcoding to Investigate Patterns of Species Utilisation in UK Shark Products Reveals Threatened Species on Sale.”